Reflective mask blank for EUV lithography and process for its production, as well as substrate with reflective layer for such mask blank and process for its production

ABSTRACT

Process for producing a substrate with reflective layer for EUVL, which comprises forming a reflective layer for reflecting EUV light on a substrate, wherein the reflective layer is a multilayer reflective film having a low refractive index layer and a high refractive index layer alternately stacked plural times by a sputtering method, and depending upon the in-plane distribution of the peak reflectivity of light in the EUV wavelength region in a radial direction from the center of the substrate at the surface of the multilayer reflective film, at least one layer among the respective layers constituting the multilayer reflective film is made to be a reflectivity distribution correction layer having a thickness distribution provided in a radial direction from the center of the substrate, to suppress the in-plane distribution of the peak reflectivity of light in the EUV wavelength region in a radial direction from the center of the substrate.

TECHNICAL FIELD

The present invention relates to a reflective mask blank for EUV (Extreme Ultraviolet) lithography (hereinafter referred to as “mask blank for EUVL” in this specification) to be used for the production of semiconductors, etc., and a process for its production.

Further, the present invention relates to a substrate with reflective layer for EUV lithography (EUVL), and a process for its production. The substrate with reflective layer for EUVL is used as a precursor for the mask blank for EUVL.

BACKGROUND ART

Heretofore, in the semiconductor industry, a photolithography method employing visible light or ultraviolet light has been used as a technique to transfer a fine pattern required to form an integrated circuit with a fine pattern on e.g. a silicon substrate. However, the conventional photolithography method has come close to its limit, while miniaturization of semiconductor devices is being accelerated. In the case of the photolithography method, the resolution limit of a pattern is about ½ of the exposure wavelength. Even if an immersion method is employed, the resolution limit is said to be about ¼ of the exposure wavelength, and even if an immersion method of ArF laser (wavelength: 193 nm) is employed, about 45 nm is presumed to be the limit. Under the circumstances, as an exposure technique for the next generation employing an exposure wavelength shorter than 45 nm, EUV lithography is expected to be prospective, which is an exposure technique employing EUV light having a wavelength further shorter than ArF laser. In this specification, EUV light is meant for a light ray having a wavelength within a soft X-ray region or within a vacuum ultraviolet region, specifically for a light ray having a wavelength of from about 10 to 20 nm, particularly about 13.5 nm±0.3 nm (from about 13.2 to 13.8 nm).

EUV light is likely to be absorbed by all kinds of substances, and the refractive index of substances at such a wavelength is close to 1, whereby it is not possible to use a conventional dioptric system like photolithography employing visible light or ultraviolet light. Therefore, in EUV lithography, a catoptric system, i.e. a combination of a reflective photomask and a mirror, is employed.

A mask blank is a stacked member before pattering, to be employed for the production of a photomask. In the case of an EUV mask blank, it has a structure wherein a reflective layer to reflect EUV light and an absorber layer to absorb EUV light, are formed in this order on a substrate made of e.g. glass.

Usually, a protective layer is formed between the above-described reflective layer and the absorber layer. Such a protective layer is one to be provided for the purpose of protecting the reflective layer, so that the reflective layer will not be damaged by an etching process to be carried out for the purpose of forming a pattern on the absorber layer.

As the reflective layer, it is common to use a multilayer reflective film having a low refractive index layer with a low refractive index to EUV light and a high refractive index layer with a high refractive index to EUV light, alternately stacked to have the light reflectivity improved when its surface is irradiated with EUV light. Specifically as such a multilayer reflective film, there is, for example, a Mo/Si multilayer reflective film having a molybdenum (Mo) layer as a low refractive index layer and a silicon (Si) layer as a high refractive index layer alternately stacked.

For the absorber layer, a material having a high absorption coefficient to EUV light, specifically e.g. a material containing chromium (Cr) or tantalum (Ta) as the main component, is used.

Usually, a protective layer is formed between the above-described reflective layer and the absorber layer. Such a protective layer is one to be provided for the purpose of protecting the reflective layer, so that the reflective layer will not be damaged by an etching process to be carried out for the purpose of forming a pattern on the absorber layer. In Patent Document 1, it is proposed to use ruthenium (Ru) as the material for the protective layer. In Patent Document 2, a protective layer is proposed which is made of a ruthenium compound (Ru content: 10 to 95 at %) containing Ru and at least one member selected from Mo, Nb, Zr, Y, B, Ti and La.

Further, as disclosed in Patent Document 3, in a mask blank for EUVL, it has been problematic that in-plane distribution of the peak reflectivity in the EUV wavelength region results at the surface of a multilayer reflective film. When a reflectivity spectrum of light in the EUV wavelength region at the surface of the multilayer reflective film is measured, the value of reflectivity varies depending upon the wavelength for measurement, and has a local maximum value i.e. the peak reflectivity. If in-plane distribution of the peak reflectivity of light in the EUV wavelength region at the surface of the multilayer reflective film (i.e. such a state that the peak reflectivity varies depending upon the locations on the multilayer reflective film) results, at the time when EUVL is carried out by using a mask for EUVL prepared from such a mask blank for EUVL, in-plane distribution of the EUV exposure amount applied to the resist on a wafer will result. This causes fluctuations in the dimension of a pattern in the exposure field and thus becomes a factor to impair high precision patterning.

In Patent Document 3, the required value relating to the in-plane uniformity of the peak reflectivity of light in the EUV wavelength region at the surface of the multilayer reflective film is set to be within ±0.25%. Further, in a case where a protective layer is formed on the multilayer reflective film, the required value relating to the in-plane uniformity of the peak reflectivity of light in the EUV wavelength region at the surface of the protective layer is set to be within ±0.25%.

Therefore, with respect to the in-plane uniformity of the peak reflectivity of light in the EUV wavelength region at the multilayer reflective film surface or at the protective layer surface, its range (the difference between the maximum value and the minimum value of the peak reflectivity) is required to be within 0.5%.

Further, as disclosed in Patent Document 3, in a mask blank for EUVL, it is also problematic that in-plane distribution of the center wavelength of reflected light, specifically, in-plane distribution of the center wavelength of reflected light in the EUV wavelength region at the multilayer reflective film surface, results. Here, the center wavelength of reflected light in the EUV wavelength region is, when the wavelengths corresponding to FWHM (full width of half maximum) of the peak reflectivity in the reflectivity spectrum in the EUV wavelength region are represented by λ1 and λ2, a wavelength that becomes the center value of these wavelengths ((λ1+λ2)/2).

In Patent Document 3, the required value relating to the in-plane uniformity of the center wavelength of reflected light in the EUV wavelength region at the surface of the multilayer reflective film is set to be within ±0.03 nm. Further, in a case where a protective layer is formed on the multilayer reflective film, the required value relating to the in-plane uniformity of the center wavelength at the surface of the protective layer is set to be within ±0.03 nm.

Therefore, with respect to the in-plane uniformity of the center wavelength of reflected light in the EUV wavelength region at the multilayer reflective film surface or at the protective layer surface, its range (the difference between the maximum value and the minimum value of the center wavelength) is required to be within 0.06 nm.

One of causes for the above in-plane distribution of reflected light at the surface of the multilayer reflective film i.e. the in-plane distribution of the peak reflectivity of light in the EUV wavelength region at the surface, and the in-plane distribution of the center wavelength of reflected light in the EUV wavelength region at the surface, is in-plane distribution of the thicknesses of the respective layers constituting the multilayer reflective film i.e. the thicknesses of low refractive index layers and high refractive index layers (Patent Document 3). Further, as disclosed in Patent Document 4, fluctuation in thickness (i.e. in-plane distribution of thickness) of a capping layer (i.e. a protective layer) to be formed on the multilayer reflective film will also be a cause for fluctuation of reflected light in the EUV wavelength region (i.e. in-plane distribution of the peak reflectivity of light in the EUV wavelength region, or in-plane distribution of the center wavelength of reflected light in the EUV wavelength region).

Therefore, at the time of film formation for the respective layers constituting the multilayer reflective film, or at the time of film formation for the protective layer, it is required to form a film uniformly in order not to bring about in-plane distribution in the film thickness.

Patent Document 5 discloses a method of forming a multilayer reflective film on a substrate, and a method of forming a capping layer on the multilayer reflective film, by means of an ion beam sputtering method. In such methods, while rotating the substrate about its center axis at the center, ion beam sputtering is carried out by maintaining the angle between the normal line to the substrate and the sputtered particles incident on the substrate to be a certain specific angle. Therefore, in the methods disclosed in Patent Document 5, as shown in FIG. 1 of the same Document, the sputtered particles will enter from an oblique direction to the normal line to the substrate. The methods are a method of forming a multilayer reflective film on a substrate having concave defects on its surface, and a method of forming a capping layer on the multilayer reflective film. However, also in a case where no concave defects are present on the substrate surface, it is desired to carry out the sputtering method under such a condition that while rotating the substrate about its center axis at the center, the sputtered particles will enter from an oblique direction to the normal line to the substrate, in order to form a film uniformly so as not to bring about in-plane distribution in the thickness of the multilayer reflective film or the capping layer to be formed on the multilayer reflective film.

PRIOR ART DOCUMENTS Patent Documents

-   Patent Document 1: JP-A-2002-122981 -   Patent Document 2: JP-A-2005-268750 -   Patent Document 3: JP-A-2009-260183 -   Patent Document 4: JP-A-2008-277398 -   Patent Document 5: JP-A-2009-510711

DISCLOSURE OF INVENTION Technical Problem

As mentioned above, heretofore, it has been considered possible to resolve not only the in-plane distribution of the center wavelength of reflected light in the EUV wavelength region but also the in-plane distribution of the peak reflectivity of light in the EUV wavelength region, at the surface of the multilayer reflective film (at the surface of the protective layer in a case where the protective layer is formed on the multilayer reflective film), by making uniform the thicknesses of the respective layers constituting the multilayer reflective film and the thickness of the protective layer in a case where the protective layer is formed on the multilayer reflective film.

However, it has been found that even in a case where the thicknesses of the respective layers constituting the multilayer reflective film (and the thickness of the protective layer in a case where the protective layer is to be formed on the multilayer reflective film) are made uniform to such a level that the range of the in-plane uniformity (the difference between the maximum value and the minimum value of the center wavelength) being within 0.06 nm is satisfied as the required value relating to the in-plane uniformity of the center wavelength of reflected light in the EUV wavelength region, there is a case where in-plane distribution exceeding the required value results in the peak reflectivity of light in the EUV wavelength region. When viewed in a radial direction from the center of the substrate on which the multilayer reflective film or the protective layer is formed, this in-plane distribution has a specific tendency, and it is an in-plane distribution such that in a radial direction of the substrate, the peak reflectivity of light in the EUV wavelength region lowers from the center of the substrate towards the peripheral portion of the substrate. Also in Examples in Patent Document 3, a reflective mirror substrate (a multilayer reflective film and substrate with protective film) obtained by forming a Mo/Si multilayer reflective film on a synthetic quartz glass substrate by an ion beam sputtering method, followed by forming a Ru film as a protective film, is confirmed to have an in-plane distribution such that the peak reflectivity at the center of the substrate is high and the peak reflectivity at the peripheral portion is low. The in-plane distribution of the peak reflectivity is 1.2%, which does not satisfy the required value relating to the in-plane uniformity of the peak reflectivity i.e. its range (the difference between the maximum value and the minimum value of the peak reflectivity) being within 0.5%.

The cause for formation of in-plane distribution with the above specific tendency is not clearly understood, but it is considered to be related with a fact that at the time of formation the respective layers constituting the multilayer reflective film or at the time of formation of the protective layer, the sputtering method is carried out under such a condition that while rotating the substrate about its center axis at the center, the sputtered particles will enter from an oblique direction to the normal line to the substrate, so that the periodical fluctuation range of the film formation rate along with the substrate rotation tends to be large from the center of the substrate towards the peripheral portion.

In order to solve such a problem of the prior art, it is an object of the present invention to provide a mask blank for EUVL excellent in the in-plane uniformity of the peak reflectivity of light in the EUV wavelength region and excellent in the in-plane uniformity of the center wavelength of reflected light in the EUV wavelength region, and a process for its production, as well as a substrate with reflective layer for EUVL to be used for the production of the mask blank for EUVL, and a process for its production.

Solution to Problem

In order to accomplish the above object, the present invention provides a process (1) for producing a substrate with reflective layer for EUV lithography (EUVL), which comprises forming a reflective layer for reflecting EUV light on a substrate, wherein the reflective layer is a multilayer reflective film having a low refractive index layer and a high refractive index layer alternately stacked plural times by a sputtering method, and depending upon the in-plane distribution of the peak reflectivity of light in the EUV wavelength region in a radial direction from the center of the substrate at the surface of the multilayer reflective film, at least one layer among the respective layers constituting the multilayer reflective film is made to be a reflectivity distribution correction layer having a thickness distribution provided in a radial direction from the center of the substrate, to suppress and reduce the in-plane distribution of the peak reflectivity of light in the EUV wavelength region in a radial direction from the center of the substrate.

Further, the present invention provides a process (2) for producing a substrate with reflective layer for EUV lithography (EUVL), which comprises forming a reflective layer for reflecting EUV light on a substrate, and forming a protective layer for the reflective layer on the reflective layer, wherein the reflective layer is a multilayer reflective film having a low refractive index layer and a high refractive index layer alternately stacked plural times by a sputtering method, the protective layer is a Ru layer or a Ru compound layer formed by a sputtering method, and depending upon the in-plane distribution of the peak reflectivity of light in the EUV wavelength region in a radial direction from the center of the substrate at the surface of the protective layer, at least one layer among the respective layers constituting the multilayer reflective film and the protective layer, is made to be a reflectivity distribution correction layer having a thickness distribution provided in a radial direction from the center of the substrate, to suppress and reduce the in-plane distribution of the peak reflectivity of light in the EUV wavelength region in a radial direction from the center of the substrate.

In the process (1) or (2) for producing a substrate with reflective layer for EUVL according to the present invention, it is preferred that the in-plane distribution of the peak reflectivity of light in the EUV wavelength region in a radial direction from the center of the substrate in a case where the thickness distribution corresponding to the reflectivity distribution correction layer is not provided, is an in-plane distribution such that the peak reflectivity becomes low in a radial direction from the center of the substrate, and as the thickness distribution in a radial direction from the center of the substrate in the reflectivity distribution correction layer, a thickness distribution such that the peak reflectivity of light in the EUV wavelength region becomes high in a radial direction from the center of the substrate, is provided, to suppress and reduce the in-plane distribution of the peak reflectivity of light in the EUV wavelength region in a radial direction from the center of the substrate.

In the process (1) or (2) for producing a substrate with reflective layer for EUVL according to the present invention, it is preferred that the thickness of the reflectivity distribution correction layer is adjusted to be such a thickness that at the peripheral portion of the substrate, the peak reflectivity of light in the EUV wavelength region becomes to have a local maximum value, and the difference between the thickness of the reflectivity distribution correction layer at the peripheral portion of the substrate and the thickness of the reflectivity distribution correction layer at the center of the substrate, is set so that the difference between the maximum value and the minimum value of the peak reflectivity in the in-plane distribution of the peak reflectivity of light in the EUV wavelength region in a radial direction from the center of the substrate in a case where the reflectivity distribution correction layer is provided, becomes to be at most 0.3%.

In the process (1) or (2) for producing a substrate with reflective layer for EUVL according to the present invention, it is preferred that the change in the peak reflectivity of light in the EUV wavelength region in a radial direction from the center of the substrate, formed by the thickness distribution in a radial direction from the center of the substrate, in the reflectivity distribution correction layer, is within 2%.

In the process (1) for producing a substrate with reflective layer for EUVL according to the present invention, it is preferred that in the multilayer reflective film, the stacked number of repeating units of the low refractive index layer and the high refractive index layer is from 30 to 60, and at least one layer among layers formed by the stacked number of repeating units being at most 20 from the uppermost layer of the multilayer reflective film, is made to be the reflectivity distribution correction layer.

In the process (2) for producing a substrate with reflective layer for EUVL according to the present invention, it is preferred that in the multilayer reflective film, the stacked number of repeating units of the low refractive index layer and the high refractive index layer is from 30 to 60, and at least one layer among the protective layer and layers formed by the stacked number of repeating units being at most 20 from the uppermost layer of the multilayer reflective film, is made to be the reflectivity distribution correction layer.

In the process (1) or (2) for producing a substrate with reflective layer for EUVL according to the present invention, it is preferred that the multilayer reflective film is a Mo/Si multilayer reflective film having a molybdenum (Mo) layer and a silicon (Si) layer alternately stacked plural times, and at least one layer among Si layers in the Mo/Si multilayer reflective film is made to be the reflectivity distribution correction layer.

In this case, it is more preferred that a Si layer as the uppermost layer among Si layers in the Mo/Si multilayer reflective film is made to be the reflectivity distribution correction layer.

Further, the present invention provides a process (1) for producing a reflective mask blank for EUV lithography (EUVL), which comprises forming a reflective layer for reflecting EUV light on a substrate, and forming an absorber layer for absorbing EUV light on the reflective layer, wherein the reflective layer is a multilayer reflective film having a low refractive index layer and a high refractive index layer alternately stacked plural times by a sputtering method, and depending upon the in-plane distribution of the peak reflectivity of light in the EUV wavelength region in a radial direction from the center of the substrate at the surface of the multilayer reflective film, at least one layer among the respective layers constituting the multilayer reflective film, is made to be a reflectivity distribution correction layer having a thickness distribution provided in a radial direction from the center of the substrate, to suppress and reduce the in-plane distribution of the peak reflectivity of light in the EUV wavelength region in a radial direction from the center of the substrate.

Further, the present invention provides a process (2) for producing a reflective mask blank for EUV lithography (EUVL), which comprises forming a reflective layer for reflecting EUV light on a substrate, forming a protective layer for the reflective layer on the reflective layer, and forming an absorber layer for absorbing EUV light on the protective layer, wherein the reflective layer is a multilayer reflective film having a low refractive index layer and a high refractive index layer alternately stacked plural times by a sputtering method, the protective layer is a Ru layer or a Ru compound layer formed by a sputtering method, and depending upon the in-plane distribution of the peak reflectivity of light in the EUV wavelength region in a radial direction from the center of the substrate at the surface of the protective layer, at least one layer among the respective layers constituting the multilayer reflective film and the protective layer, is made to be a reflectivity distribution correction layer having a thickness distribution provided in a radial direction from the center of the substrate, to suppress and reduce the in-plane distribution of the peak reflectivity of light in the EUV wavelength region in a radial direction from the center of the substrate.

In the process (1) or (2) for producing a reflective mask blank for EUVL according to the present invention, a low reflective layer for inspection light to be used for inspection of a mask pattern may be further formed on the absorber layer.

In the process (1) or (2) for producing a reflective mask blank for EUVL according to the present invention, it is preferred that the in-plane distribution of the peak reflectivity of light in the EUV wavelength region in a radial direction from the center of the substrate in a case where the thickness distribution corresponding to the reflectivity distribution correction layer is not provided, is an in-plane distribution such that the peak reflectivity becomes low in a radial direction from the center of the substrate, and as the thickness distribution in a radial direction from the center of the substrate in the reflectivity distribution correction layer, a thickness distribution such that the peak reflectivity of light in the EUV wavelength region becomes high in a radial direction from the center of the substrate, is provided, to suppress and reduce the in-plane distribution of the peak reflectivity of light in the EUV wavelength region in a radial direction from the center of the substrate.

In the process (1) or (2) for producing a reflective mask blank for EUVL according to the present invention, it is preferred that the thickness of the reflectivity distribution correction layer is adjusted to be such a thickness that at the peripheral portion of the substrate, the peak reflectivity of light in the EUV wavelength region becomes to have a local maximum value, and the difference between the thickness of the reflectivity distribution correction layer at the peripheral portion of the substrate and the thickness of the reflectivity distribution correction layer at the center of the substrate, is set so that the difference between the maximum value and the minimum value of the peak reflectivity in the in-plane distribution of the peak reflectivity of light in the EUV wavelength region in a radial direction from the center of the substrate in a case where the reflectivity distribution correction layer is provided, becomes to be at most 0.3%.

In the process (1) or (2) for producing a reflective mask blank for EUVL according to the present invention, it is preferred that the change in the peak reflectivity of light in the EUV wavelength region in a radial direction from the center of the substrate, formed by the thickness distribution in a radial direction from the center of the substrate, in the reflectivity distribution correction layer, is within 2%.

In the process (1) for producing a reflective mask blank for EUVL according to the present invention, it is preferred that in the multilayer reflective film, the stacked number of repeating units of the low refractive index layer and the high refractive index layer is from 30 to 60, and at least one layer among layers formed by the stacked number of repeating units being at most 20 from the uppermost layer of the multilayer reflective film, is made to be the reflectivity distribution correction layer.

In the process (2) for producing a reflective mask blank for EUVL according to the present invention, it is preferred that in the multilayer reflective film, the stacked number of repeating units of the low refractive index layer and the high refractive index layer is from 30 to 60, and at least one layer among the protective layer and layers formed by the stacked number of repeating units being at most 20 from the uppermost layer of the multilayer reflective film, is made to be the reflectivity distribution correction layer.

In the process (1) or (2) for producing a reflective mask blank for EUVL according to the present invention, it is preferred that the multilayer reflective film is a Mo/Si multilayer reflective film having a molybdenum (Mo) layer and a silicon (Si) layer alternately stacked plural times, and at least one layer among Si layers in the Mo/Si multilayer reflective film is made to be the reflectivity distribution correction layer.

In this case, it is more preferred that a Si layer as the uppermost layer among Si layers in the Mo/Si multilayer reflective film is made to be the reflectivity distribution correction layer.

Further, the present invention provides a substrate with reflective layer for EUVL, produced by the process (1) or (2) for producing a substrate with reflective layer for EUVL according to the present invention.

Further, the present invention provides a reflective mask blank for EUVL, produced by the process (1) or (2) for producing a reflective mask blank for EUVL according to the present invention.

Further, the present invention provides a substrate with reflective layer (1) for EUV lithography (EUVL), which comprises a substrate and a reflective layer for reflecting EUV light formed on the substrate, wherein the reflective layer is a multilayer reflective film having a low refractive index layer and a high refractive index layer alternately stacked plural times, and at least one layer among the respective layers constituting the multilayer reflective film is a reflectivity distribution correction layer having a thickness distribution such that the thickness increases or decreases within a range of from 0.1 to 1 nm in a radial direction from the center of the substrate.

Further, the present invention provides a substrate with reflective layer (2) for EUV lithography (EUVL), which comprises a substrate, a reflective layer for reflecting EUV light formed on the substrate, and a protective layer for the reflective layer formed on the reflective layer, wherein the reflective layer is a multilayer reflective film having a low refractive index layer and a high refractive index layer alternately stacked plural times, and at least one layer among the respective layers constituting the multilayer reflective film and the protective layer is a reflectivity distribution correction layer having a thickness distribution such that the thickness increases or decreases within a range of from 0.1 to 1 nm in a radial direction from the center of the substrate.

In the substrate with reflective layer (1) or (2) for EUVL according to the present invention, it is preferred that the multilayer reflective film is a Mo/Si multilayer reflective film having a molybdenum (Mo) layer and a silicon (Si) layer alternately stacked plural times, and at least one layer among Si layers in the Mo/Si multilayer reflective film is the reflectivity distribution correction layer.

In this case, it is more preferred that a Si layer as the uppermost layer among Si layers in the Mo/Si multilayer reflective film is the reflectivity distribution correction layer.

Further, the present invention provides a reflective mask blank (1) for EUV lithography (EUVL), which comprises a substrate, a reflective layer for reflecting EUV light formed on the substrate, and an absorber layer for absorbing EUV light formed on the reflective layer, wherein the reflective layer is a multilayer reflective film having a low refractive index layer and a high refractive index layer alternately stacked plural times, and at least one layer among the respective layers constituting the multilayer reflective film is a reflectivity distribution correction layer having a thickness distribution such that the thickness increases or decreases within a range of from 0.1 to 1 nm in a radial direction from the center of the substrate.

Further, the present invention provides a reflective mask blank (2) for EUV lithography (EUVL), which comprises a substrate, a reflective layer for reflecting EUV light formed on the substrate, a protective layer for the reflective layer formed on the reflective layer, and an absorber layer for absorbing EUV light formed on the protective layer, wherein the reflective layer is a multilayer reflective film having a low refractive index layer and a high refractive index layer alternately stacked plural times, the protective layer is a Ru layer or a Ru compound layer, and at least one layer among the respective layers constituting the multilayer reflective film and the protective layer is a reflectivity distribution correction layer having a thickness distribution such that the thickness increases or decreases within a range of from 0.1 to 1 nm in a radial direction from the center of the substrate.

In the reflective mask blank (1) or (2) for EUVL according to the present invention, it is preferred that the multilayer reflective film is a Mo/Si multilayer reflective film having a molybdenum (Mo) layer and a silicon (Si) layer alternately stacked plural times, and at least one layer among Si layers in the Mo/Si multilayer reflective film is the reflectivity distribution correction layer.

In this case, it is more preferred that a Si layer as the uppermost layer among Si layers in the Mo/Si multilayer reflective film is the reflectivity distribution correction layer.

In the reflective mask blank (1) or (2) for EUVL according to the present invention, a low reflective layer for inspection light to be used for inspection of a mask pattern may be formed on the absorber layer.

Further, the present invention provides a reflective mask for EUV lithography obtained by patterning the reflective mask blank (1) or (2) for EUVL according to the present invention.

Advantageous Effects of Invention

According to the present invention, it is possible to produce a reflective mask blank for EUVL and a substrate with reflective layer for EUVL, excellent in the in-plane uniformity of the peak reflectivity of light in the EUV wavelength region and in the in-plane uniformity of the center wavelength of reflected light in the EUV wavelength region, at the surface of the multilayer reflective film.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic cross-sectional view illustrating an embodiment of the reflective mask blank for EUVL to be produced by the process of the present invention.

FIG. 2 is an illustrative view showing the procedure for spin film formation.

FIG. 3 is a graph showing the relation between the thickness of the uppermost Si layer in a Mo/Si multilayer reflective film and the peak reflectivity of light in the EUV wavelength region at the surface of the Mo/Si multilayer reflective film.

FIG. 4 is a schematic cross-sectional view illustrating another embodiment of the reflective mask blank for EUVL to be produced by the process of the present invention.

FIG. 5 is a graph showing the relation between the location in a radial direction from the center of the substrate and the in-plane distribution of the peak reflectivity of light in the EUV wavelength region at the surface of a Mo/Si multilayer reflective film, in Comparative Example 1 and Example 1. “Before correction” represents the results in Comparative Example 1 and “After correction” represents the results in Example 1.

FIG. 6 is a graph showing the relation between the location in a radial direction from the center of the substrate and the in-plane distribution of the peak reflectivity of light in the EUV wavelength region at the surface of a Mo/Si multilayer reflective film, in Comparative Example 2 and Example 2. “Before correction” represents the results in Comparative Example 2 and “After correction” represents the results in Example 2.

FIG. 7 is a graph showing the relation between the location in a radial direction from the center of the substrate and the in-plane distribution of the peak reflectivity of light in the EUV wavelength region at the surface of a Mo/Si multilayer reflective film, in Comparative Example 3 and Example 3. “Before correction” represents the results in Comparative Example 3 and “After correction” represents the results in Example 3.

FIG. 8 is a graph showing the relation between the location in a radial direction from the center of the substrate and the in-plane distribution of the peak reflectivity of light in the EUV wavelength region at the surface of a Mo/Si multilayer reflective film, in Comparative Example 4 and Example 4. “Before correction” represents the results in Comparative Example 4 and “After correction” represents the results in Example 4.

DESCRIPTION OF EMBODIMENTS

Now, the present invention will be described with reference to the drawings.

FIG. 1 is a schematic cross-sectional view illustrating an embodiment of the reflective mask blank for EUVL to be produced by the process of the present invention (hereinafter referred to as “the reflective mask blank for EUVL of the present invention” in this specification). The reflective mask blank 1 for EUVL shown in FIG. 1 has a reflective layer 12 for reflecting EUV light and an absorber layer 14 for absorbing EUV light formed in this order on a substrate 11. Between the reflective layer 12 and the absorber layer 14, a protective layer 13 is formed for protecting the reflective layer 12 during formation of a pattern in the absorber layer 14.

Here, in the reflective mask blank for EUVL of the present invention, in the construction as shown in FIG. 1, only the substrate 11, the reflective layer 12 and the absorber layer 14 are essential, and the protective layer 13 is an optional constituting element.

Now, the individual constituting elements of the reflective mask blank 1 for EUVL will be described.

The substrate 11 is required to satisfy the properties as a substrate for a reflective mask blank for EUVL.

Therefore, the substrate 11 is preferably one having a low thermal expansion coefficient (preferably 0±1.0×10⁻⁷/° C., more preferably 0±0.3×10⁻⁷/° C., further preferably 0±0.2×10⁻⁷/° C., still further preferably 0±0.1×10⁻⁷/° C., particularly preferably 0±0.05×10⁻⁷/° C.) and being excellent in smoothness, planarity and durability against a cleaning liquid to be used for e.g. cleaning a mask blank or a photomask after patterning. As the substrate 11, specifically, a glass having a low thermal expansion coefficient, such as a SiO₂—TiO₂ type glass, may be used. However, the substrate is not limited thereto, and it is possible to employ a substrate of e.g. crystallized glass having β-quartz solid solution precipitated, quartz glass, silicon, or a metal. Further, a film such as a stress correcting film may be formed on the substrate 11.

The substrate 11 preferably has a smooth surface having a surface roughness of at most 0.15 nm rms and a flatness of at most 100 nm, whereby a high reflectivity and transfer precision can be attained by a photomask after forming a pattern.

The size, thickness, etc. of the substrate 11 may suitably be determined depending upon e.g. the designed values for the mask. In Examples given hereinafter, a SiO₂—TiO₂ type glass having a size of 6 inches (152 mm) square and a thickness of 0.25 inch (6.35 mm) was used.

It is preferred that no defect is present on the film-forming surface of the substrate 11 i.e. the surface of the substrate 11 on the side where a reflective layer 12 is to be formed. However, even in a case where a defect is present, in order not to cause a phase defect due to a concave defect and/or a convex defect, it is preferred that the depth of a concave defect or the height of a convex defect is not more than 2 nm, and the half value width of such a concave defect or convex defect is not more than 60 nm.

The property particularly required for the reflective layer 12 of the reflective mask blank for EUVL is a high EUV light reflectivity. Specifically, when a light ray within the EUV wavelength region is applied at an incident angle of 6° to the surface of the reflective layer 12, the peak reflectivity of light in the EUV wavelength region (i.e. the local maximum value of the reflectivity of the light ray in the vicinity of a wavelength of 13.5 nm, which will be hereinafter referred to as “the peak reflectivity of the EUV light” in this specification) is preferably at least 60%, more preferably at least 63%, further preferably at least 65%. Further, even in a case where a protective layer 13 is formed on the reflective layer 12, the peak reflectivity of the EUV light is preferably at least 60%, more preferably at least 63%, further preferably at least 65%.

Further, for the reflective layer 12 of the reflective mask blank for EUVL, the required value of the in-plane uniformity of the peak reflectivity of the EUV light is within 0.5% as its range (the difference between the maximum value and the minimum value of the peak reflectivity). Further, in a case where a protective layer 13 is formed on the reflective layer 12, the required value of the in-plane uniformity of the peak reflectivity of the EUV light at the surface of the protective layer 13 is within 0.5% as its range (the difference between the maximum value and the minimum value of the peak reflectivity).

Further, for the reflective layer 12 of the reflective mask blank for EUVL, the required value of the in-plane uniformity of the center wavelength of reflected light in the EUV wavelength region is within 0.06 nm as its range (the difference between the maximum value and the minimum value of the center wavelength). Further, in a case where a protective layer 13 is formed on the reflective layer 12, the required value of the in-plane uniformity of the center wavelength of reflected light in the EUV wavelength region at the surface of the protective layer 13 is within 0.06 nm as its range (the difference between the maximum value and the minimum value of the peak reflectivity).

As a reflective layer of a reflective mask blank for EUVL, a multilayer reflective film having a low refractive index layer as a layer to show a low refractive index to EUV light and a high refractive index layer as a layer to show a high refractive index to EUV light alternately stacked plural times is widely used, since a high reflectivity can thereby be accomplished in the EUV wavelength region. As such a multilayer reflective film, a Mo/Si multilayer reflective film having a molybdenum (Mo) layer as a low refractive index layer and a silicon (Si) layer as a high refractive index layer alternately stacked plural times, is usually employed. Other examples of the multilayer reflective film may, for example, be a Ru/Si multilayer reflective film having a ruthenium (Ru) layer as a low refractive index layer and a silicon (Si) layer as a high refractive index layer alternately stacked plural times, a Mo/Be multilayer reflective film having a molybdenum (Mo) layer as a low refractive index layer and a berylium (Be) layer as a high refractive index layer alternately stacked plural times, and a Mo compound/Si compound multilayer reflective film having a molybdenum (Mo) compound layer as a low refractive index layer and a silicon (Si) compound layer as a high refractive index layer alternately stacked plural times.

Further, like a multilayer reflective film disclosed in JP-A-2006-093454, the multilayer reflective film may be one having an interlayer such as a diffusion preventive layer or a film stress relaxation layer formed between the low refractive index layer (Mo layer) and the high refractive index layer (Si layer).

The thickness of the respective layers (a low refractive index layer and a high refractive index layer) constituting the multilayer reflective film, and the stacked number of repeating units of the low refractive index layer and the high refractive index layer, vary depending upon the constituting materials for the respective layers or the EUV light reflectivity to be accomplished. In the case of the Mo/Si multilayer reflective film, however, in order to obtain a reflective layer 12 having an EUV light peak reflectivity of at least 60%, for example, a Mo layer having a thickness of 2.5 nm and a Si layer having a thickness of 4.5 nm are stacked so that the stacked number of repeating units would be from 30 to 60.

Further, the respective layers (a Mo layer and a Si layer) constituting the Mo/Si multilayer reflective film are adjusted so that (1) the thickness distribution of the respective layers is a uniform thickness distribution within from 0.4 to 0.3% from the requirement for the after-mentioned wavelength distribution, (2) the respective thicknesses of the Mo layer and the Si layer are adjusted to be thicknesses whereby the maximum reflectivity is obtainable from the adjustment of the after-mentioned γ ratio, and (3) the total thickness (bilayer) of the Mo layer and the Si layer is adjusted to be about 7 nm so that the center wavelength of reflected light in the EUV wavelength region will be about 13.5 nm.

Here, the respective layers (a low refractive index layer and a high refractive index layer) constituting the multilayer reflective film may be formed to have desired thicknesses by means of a sputtering method such as a magnetron sputtering method or an ion beam sputtering method. For example, in the case of forming a Mo/Si multilayer reflective film by means of an ion beam sputtering method, it is preferred that a Mo layer is formed to have a thickness of 2.5 nm at an ion accelerating voltage of from 300 to 1,500 V and a film-deposition rate of from 1.8 to 18.0 nm/min by using a Mo target as the target and an Ar gas (gas pressure: 1.3×10⁻² Pa to 2.7×10⁻² Pa) as the sputtering gas, and then, a Si layer is formed to have a thickness of 4.5 nm at an ion accelerating voltage of from 300 to 1,500 V and a film-deposition rate of from 1.8 to 18.0 nm/min by using a Si target as the target and an Ar gas (gas pressure: 1.3×10⁻² Pa to 2.7×10⁻² Pa) as the sputtering gas. When this operation is taken as one cycle, the Mo/Si multilayer reflective film is formed by stacking the Mo layer and the Si layer by from 30 to 60 cycles.

However, in order to satisfy the above-mentioned required value of the in-plane uniformity of the peak reflectivity of EUV light and the required value relating to the in-plane uniformity of the center wavelength of reflected light in the EUV wavelength region, it is required to form a film uniformly so as not to cause in-plane distribution in the thicknesses of the respective layers (a low refractive index layer and a high refractive index layer) constituting the multilayer reflective film.

In order to form the respective layers (a low refractive index layer and a high refractive index layer) constituting the multilayer reflective film to have uniform thicknesses by means of a sputtering method such as a magnetron sputtering method or an ion beam sputtering method, it is preferred that as shown in FIG. 2, while a substrate 11 is rotated about an axis (center axis) 30 passing through its center O, sputtered particles 20 are permitted to enter from an oblique direction to the normal line H to the substrate 11. The reason is such that it is possible to make the thickness of each layer formed by the sputtering method uniform by adjusting the incident angle α of the sputtered particles 20 to the normal line H.

Hereinafter, in this specification, the film-forming procedure as shown in FIG. 2 will be referred to as “spinning film formation”. Here, the center axis is an axis passing through the center of the substrate, and in a case where the substrate shape is circular like the substrate 11 shown in FIG. 2, the center axis is an axis passing through the center O of the circle, and in a case where the substrate shape is a square or rectangle, the center axis is an axis passing through the intersection of diagonal lines of the square or rectangle.

In the foregoing, a method for carrying out film formation on a single substrate has been exemplified. However, the method is not limited thereto and may be a so-called a plural substrate film-forming method wherein film formation is carried out simultaneously on plural substrates. In the case of the plural substrate film-forming method, it is preferred to set the film-forming conditions which include not only rotation of substrates about their central axes but also movement of revolution of the substrates.

At the time of forming the respective layers (a low refractive index layer and a high refractive index layer) constituting the multilayer reflective film, it is possible to uniformly control the thicknesses of the respective layers to be formed by the sputtering method, by carrying out a spinning film formation as shown in FIG. 2 and adjusting the incident angle α of sputtered particles 20 to the normal line H.

With respect to the required value relating to the in-plane uniformity of the center wavelength of reflected light in the EUV wavelength region, it is shown in Comparative Example 1 given hereinafter that the respective layers of the Mo/Si multilayer reflective film are uniformly formed to such an extent that its range (the difference between the maximum value and the minimum value of the center wavelength) being within 0.06 nm is satisfied. In Comparative Example 1, the in-plane distribution of the center wavelength of reflected light in the EUV wavelength region is within 0.04 nm, which satisfies its range being within 0.06 nm as the required value relating to the in-plane uniformity of the center wavelength of reflected light in the EUV wavelength region. Here, the above in-plane distribution (within 0.04 nm) of the center wavelength of reflected light in the EUV wavelength region corresponds to 0.04/13.53≈0.3% as the thickness distribution of a bilayer composed of two layers of the Mo layer and the Si layer as the basic construction of the Mo/Si multilayer film.

However, even in a case where the thicknesses of the respective layers of the Mo/Si multilayer reflective film are uniformly formed to such a level that with respect to the required value relating to the in-plane uniformity of the center wavelength of reflected light in the EUV wavelength region, its range being within 0.06 nm is satisfied, there may be a case where in-plane distribution exceeding the require value results in the peak reflectivity of EUV light. This is shown in Comparative Example 1 given hereinafter (by a dashed line corresponding to “Before correction” in FIG. 5).

In FIG. 5, in-plane distribution is shown such that the peak reflectivity of EUV light lowers from the center of the substrate towards the peripheral portion of the substrate. The in-plane distribution of the peak reflectivity of EUV light exceeds 0.6% and as such does not satisfy the required value relating to in-plane uniformity of the peak reflectivity i.e. its range (the difference between the maximum value and the minimum value of the peak reflectivity) being within 0.5%.

In the present invention, at least one layer among the respective layers (low refractive index layers and high refractive index layers) constituting the multilayer reflective film is made to be a reflectivity distribution correction layer having a thickness distribution provided in a radial direction from the center of the substrate, to suppress the in-plane distribution of the peak reflectivity of EUV light i.e. the in-plane distribution such that the peak reflectivity of EUV light lowers from the center of the substrate towards the peripheral portion of the substrate. Therefore, in the reflectivity distribution correction layer, thickness distribution is provided so that the peak reflectivity of EUV light increases from the center of the substrate towards the peripheral portion of the substrate.

In this specification, the peripheral portion of the substrate is meant for a peripheral portion of a region (an optical property evaluation region) for evaluation of an optical property of the multilayer reflective film, such as the peak reflectivity of EUV light or the center wavelength of reflected light in the EUV wavelength region. For example, in the case of a substrate of a 152 mm square, its optical property evaluation region is a region of a 142 mm square. The corner portions of this region of a 142 mm square are located in the vicinity of 100 mm in a radial direction from the center of the substrate, and therefore, the peripheral portion of the substrate is located in the vicinity of 100 mm in a radial direction from the center of the substrate.

The reason as to why at least one layer among the respective layers (low refractive index layers and high refractive index layers) constituting the multilayer reflective film is made to be a reflectivity distribution correction layer having a thickness distribution provided in a radial direction from the center of the substrate, for the above mentioned purpose of suppressing the in-plane distribution of the peak reflectivity of EUV light, is that, as shown in FIG. 3, the peak reflectivity of EUV light at the surface of the multilayer reflective film, has a dependency on the thickness of each layer (a low refractive index layer or a high refractive index layer) constituting the multilayer reflective film.

FIG. 3 is a graph showing the relation between the film thickness of a Si layer as the outermost layer among the respective layers constituting the Mo/Si multilayer reflective film formed by repeating stack of Mo and Si alternately for 40 cycles, and the peak reflectivity of EUV light at the surface of the Mo/Si multilayer reflective film. Here, the thickness of Mo is 2.5 nm, and the thickness of Si except for the uppermost layer is 4.5 nm.

As shown in FIG. 3, the peak reflectivity of EUV light at the surface of the Mo/Si multilayer reflective film, has a dependency on the thickness of the Si layer, and repeats rise and fall periodically between the local maximum value and the local minimum value. In FIG. 3, the relation between the film thickness of a Si layer as the outermost layer among the respective layers constituting the Mo/Si multilayer reflective film and the peak reflectivity of EUV light at the surface of the Mo/Si multilayer reflective film, is shown, but the peak reflectivity of EUV light at the surface of the Mo/Si multilayer reflective film also has a dependency on the thickness of a Si layer other than the outermost layer and repeats rise and fall periodically between the local maximum value and the local minimum value. The peak reflectivity of EUV light at the surface of the Mo/Si multilayer reflective film also has a dependency on the thickness of a Mo layer and repeats rise and fall periodically between the local maximum value and the local minimum value.

Further, in FIG. 3, with respect to a Mo/Si multilayer reflective film, the relation between the thickness of the Si layer as the uppermost layer and the peak reflectivity of EUV light at the surface of the Mo/Si multilayer reflective film, is shown, but also in a multilayer reflective film wherein the above-mentioned low refractive index layer and high refractive index layer are different from the Mo/Si multilayer reflective film, or one wherein a diffusion preventive layer is formed between the low refractive index layer and the high refractive index layer of the multilayer reflective film, the peak reflectivity of EUV light at the surface of the multilayer reflective film, has a dependency on the thickness of each layer (a low refractive index layer or a high refractive index layer) constituting the multilayer reflective film.

In the present invention, in order to suppress the above-mentioned in-plane distribution of the peak reflectivity of EUV light i.e. the in-plane distribution wherein the peak reflectivity of EUV light lowers from the center of the substrate towards the peripheral portion of the substrate, at least one layer among the respective layers (low refractive index layers and high refractive index layers) constituting the multilayer reflective film, is made to be a reflectivity distribution correction layer having a thickness distribution provided to increase the peak reflectivity in a radial direction from the center of the substrate (in other words, a thickness distribution so that the peak reflectivity lowers from the peripheral portion towards the center of the substrate).

The thickness distribution to increase the peak reflectivity in a radial direction from the center of the substrate may be set based on the above-mentioned in-plane distribution of the peak reflectivity at the surface of the multilayer reflective film and the above-mentioned thickness dependency in the layer being the reflectivity distribution correction layer (the thickness dependency shown in FIG. 3 in a case where the Si layer as the uppermost layer of the Mo/Si multilayer reflective film is made to be the reflectivity distribution correction layer).

In the present invention, a thickness distribution is provided to lower the peak reflectivity of EUV light from the peripheral portion of a substrate towards the center of the substrate, and therefore, the thickness of the reflectivity distribution correction layer at the peripheral portion of the substrate is made to be in the vicinity of the thickness at which the peak reflectivity of EUV light becomes to have a local maximum value. In Examples given hereinafter, the thickness of the reflectivity distribution correction layer (the Si layer as the uppermost layer in the Mo/Si multilayer reflective film) was made to be 4.5 nm based on FIG. 3.

And, a thickness distribution may be provided in a radial direction so that the thickness of the reflectivity distribution correction layer increases or decreases towards the center of the substrate. Here, with a view to suppressing the above-mentioned in-plane distribution of the peak reflectivity of EUV light, in a case where a thickness distribution is provided in a radial direction from the center of the substrate, it is preferred to set the difference between the thickness at the peripheral portion of the substrate and the thickness at the center of the substrate, so that the difference between the maximum value and the minimum value of the peak reflectivity becomes to be at most 0.3% in the in-plane distribution of the peak reflectivity of EUV light in a radial direction from the center of the substrate.

As mentioned above, in the case of Comparative Example 1 given hereinafter, the amount of decrease in the peak reflectivity from the center towards the peripheral portion of the substrate (the amount of decrease in the peak reflectivity to the maximum value of the peak reflectivity) as derived from the in-plane distribution of the peak reflectivity shown in FIG. 5 becomes to be about 0.6%.

Therefore, the thickness at the center of the substrate may be set so that in FIG. 3, the amount of decrease in the peak reflectivity to the local maximum value of the peak reflectivity will be about 0.6%.

Based on these premises, in Example 1, a thickness distribution in a radial direction was set so that the thickness of the Si layer as the uppermost layer in the Mo/Si multilayer reflective film became to be 4.5 nm at the peripheral portion of the substrate, and the thickness of the Si layer as the uppermost layer in the Mo/Si multilayer reflective film became to be 4.9 nm at the center of the substrate.

Here, in order to provide the above thickness distribution to the Si layer as the uppermost layer of the Mo/Si multilayer reflective film, at the time of carrying out the spinning film formation as shown in FIG. 2, the incident angle α of sputtered particles 20 to the normal line H may suitably be adjusted. For example, when the incident angle of sputtered particles 20 at the time of a usual film formation is taken as the standard, the incident angle of sputtered particles 20 at the time of forming the reflection distribution correction layer may be adjusted by giving a difference of at least 10°, or in the case of imparting a thickness distribution of at least 10%, the incident angle of sputtered particles 20 at the time of forming the reflection distribution correction layer may be adjusted by giving a difference of at least 20°. Further, in Examples given hereinafter, the incident angle α was adjusted within a range of from 0° to 60° to obtain a desired thickness distribution, and the in-plane distribution of the peak reflectivity of EUV light was confirmed to be at most 0.3%.

However, if the change in the peak reflectivity of EUV light caused by providing a thickness distribution in a radial direction from the center of the substrate, is too large, an in-plane distribution is rather likely to be created in the peak reflectivity of EUV light. Therefore, the change in the peak reflectivity of EUV light caused by providing a thickness distribution in a radial direction from the center of the substrate is preferably at most 2%, more preferably at most 1.5%, further preferably at most 1%.

As described above, in the present invention, at least one layer among the respective layers (low refractive index layers and high refractive index layers) constituting the multilayer reflective film, is made to be a reflectivity distribution correction layer having a thickness distribution provided to increase the peak reflectivity of EUV light in a radial direction from the center of the substrate (in other words, a thickness distribution so that the peak reflectivity of EUV light lowers from the peripheral portion of the substrate towards the center of the substrate).

Therefore, any layer constituting the multilayer reflective film may be made to be the above reflectivity distribution correction layer having a thickness distribution provided. That is, a high refractive index layer (Si layer) may be made to be the above reflectivity distribution correction layer having a thickness distribution provided, or a low refractive index layer (Mo layer) may be made to be the above reflectivity distribution correction layer having a thickness distribution provided.

Further, among the respective layers constituting the multilayer reflective film, only one layer may be made to be the above reflectivity distribution correction layer having a thickness distribution provided, or two or more layers may be made to be such reflectivity distribution correction layers having a thickness distribution provided. Therefore, both of a high refractive index layer (Si layer) and a low refractive index layer (Mo layer) may be made to be such reflectivity distribution correction layers. Further, in a case where two or more layers are made to be such reflectivity distribution correction layers having a thickness distribution provided, mutually continuous two or more layers may be made to be such reflectivity distribution correction layers having a thickness distribution provided, or mutually separated two or more layers may be made to be such reflectivity distribution correction layers having a thickness distribution provided.

Here, among the respective layers constituting the multilayer reflective film, such a layer having a thickness distribution provided, is an exception to the above mentioned one construction example of a high refractive index layer (Mo layer) and a low refractive index layer (Si layer) ((2.5 nm) and (4.5 nm)).

However, when a layer closer to the surface of the multilayer reflective film is made to be such a layer having a thickness distribution provided, the peak reflectivity of EUV light at the surface of the multilayer reflective film tends to change more in many cases. Therefore, it is preferred that at least one layer among layers formed by the stacked number of repeating units of a low refractive index layer (Mo layer) and a high refractive index layer (Si layer) being at most 20 from the uppermost layer of the multilayer reflective film, is made to be the above reflectivity distribution correction layer, it is more preferred that at least one layer among layers formed by the stacked number of repeating units being at most 10, is made to be the above reflectivity distribution correction layer having a thickness distribution provided, and it is further preferred that at least one layer among layers formed by the stacked number of repeating units being at most 5, is made to be the above reflectivity distribution correction layer having a thickness distribution provided.

Here, the stacked number of repeating units of a Mo layer and a Si layer in the Mo/Si multilayer reflective film is from 30 to 60, as mentioned above.

In the case of the Mo/Si multilayer reflective film, it is preferred that among the layers constituting the Mo/Si multilayer reflective film, a Si layer is made to be the above reflectivity distribution correction layer having a thickness distribution provided. In thickness of the respective layers constituting the Mo/Si multilayer reflective film, the Si layer is thicker than the Mo layer, as shown in the above-mentioned one construction example (Mo layer (2.5 nm), Si layer (4.5 nm)). The reason is that such a combination is preferred as the γ ratio (the ratio of the Si layer to the cycle length) to increase the peak reflectivity of EUV light. And, the Si layer having a larger thickness is capable of changing the peak reflectivity of EUV light at the surface of the Mo/Si multilayer reflective film by a smaller change in thickness distribution, whereby the thickness distribution can easily be adjusted within a control range of the film-forming apparatus, such being preferred. In a case where the reflection distribution correction layer is to be made of only one Si layer, when the uppermost Si layer is counted as the first layer, the reflection distribution correction layer may be made of only one Si layer among the first to 30th layers (the 30th to 60th layers depending upon the stacked number of repeating units of the Mo layer and the Si layer), preferably only one Si layer among the first to 20th layer, more preferably only one Si layer among the first to 10th layer, further preferably only one Si layer among the first to 5th layer, still further preferably only one Si layer among the first to third layers. Here, the above layer numbers of Si layers are layer numbers when Mo layers are not counted. For example, in the case of the Mo/Si multilayer reflective film wherein the uppermost layer is a Si layer, the second Si layer corresponds to the Si layer following the uppermost Si layer and Mo layer.

Further, in the Mo/Si multilayer reflective film, for example in a case where only the uppermost (first) Si layer is made to be the reflectivity distribution correction layer, it is only required to change a condition such as the incident angle of sputtered particles from the condition for film formation of other Si layers, only at the time of the final film formation in the sputtering process, whereby there is a merit in that the film-forming process will not be cumbersome.

The protective layer 13 is provided for the purpose of protecting the reflective layer 12, so that at the time of forming a pattern in an absorber layer 14 by an etching process, specifically a dry etching process employing a chlorine-type gas as an etching gas, the reflective layer 12 will not be damaged by the etching process. Accordingly, as the material for the protective layer 13, a material hardly susceptible to an influence by the etching process of the absorber layer 14 i.e. having an etching rate slower than the absorber layer 14 and hardly susceptible to damage by such an etching process, is selected for use.

Further, the protective layer 13 is preferably configured such that the protective layer 13 itself also has a high EUV light reflectivity in order not to impair the EUV light reflectivity at the reflective layer 12 even after forming the protective layer 13.

In the present invention, in order to satisfy the above conditions, as the protective layer 13, a Ru layer or a Ru compound layer is formed. The Ru compound is preferably constituted by at least one member selected from the group consisting of RuB, RuNb and RuZr. In a case where the protective layer 13 is a Ru compound layer, the content of Ru is preferably at least 50 at %, more preferably at least 80 at %, particularly preferably at least 90 at %. However, in a case where the protective layer 13 is a RuNb layer, the content of Nb in the protective layer 13 is preferably from 5 to 40 at %, particularly preferably from 5 to 30 at %.

In a case where a protective layer 13 is formed on the reflective layer 12, the surface roughness of the surface of the protective layer 13 is preferably at most 0.5 nm rms. If the surface roughness of the surface of the protective layer 13 is large, the surface roughness of the absorber layer 14 to be formed on the protective layer 13 tends to be large, whereby the edge roughness of a pattern to be formed on the absorber layer 14 tends to be large, and the dimensional precision of the pattern tends to be poor. As the pattern becomes fine, the influence of the edge roughness becomes distinct, and therefore, it is required that the surface of the absorber layer 14 is smooth.

When the surface roughness of the surface of the protective layer 13 is at most 0.5 nm rms, the surface of the absorber layer 14 to be formed on the protective layer 13 will be sufficiently smooth, thus being free from deterioration of the dimensional precision of a pattern due to an influence of the edge roughness. The surface roughness of the surface of the protective layer 13 is more preferably at most 0.4 nm rms, further preferably at most 0.3 nm rms.

In a case where the protective layer 13 is formed on the reflective layer 12, the thickness of the protective layer 13 is preferably from 1 to 10 nm in that it is thereby possible to increase the EUV light reflectivity and to obtain an etching resistance property. The thickness of the protective layer 13 is more preferably from 1 to 5 nm, further preferably from 2 to 4 nm.

Further, in a case where the protective layer 13 is formed on the reflective layer (multilayer reflective film) 12, the above mentioned thickness distribution in a radial direction from the center of the substrate is provided to at least one layer among the protective layer and the respective layers (low refractive index layers and high refractive index layers) constituting the multilayer reflective film. Therefore, the above thickness distribution may be provided to only the Ru layer or the Ru compound layer formed as the protective layer 13. Otherwise, the above thickness distribution may be provided to both of the Ru layer or the Ru compound layer, and the respective layers (low refractive index layers and high refractive index layers) constituting the multilayer reflective film.

However, in a case where the reflective layer 12 is a Mo/Si multilayer reflective film, it is preferred to make the thickness of a Si layer larger than the thickness of the Ru layer or the Ru compound layer formed as the protective layer 13, in order to increase the EUV light reflectivity, and therefore, also in a case where the protective layer 13 is formed on the reflective layer (Mo/Si multilayer reflective film) 12, it is preferred to provide the thickness distribution to a Si layer constituting the Mo/Si multilayer reflective film.

In the case of forming the protective layer 13 on the reflective layer 12, the protective layer 13 is formed by means of a sputtering method such as a magnetron sputtering method or an ion beam sputtering method.

In a case where a Ru layer is to be formed as the protective layer 13 by means of an ion beam sputtering method, discharge may be made in an inert gas atmosphere containing at least one of helium (He), argon (Ar), neon (Ne), krypton (Kr) and xenon (Xe) by using a Ru target as the target. Specifically, the ion beam sputtering may be carried out under the following conditions.

Sputtering gas: Ar (gas pressure: from 1.3×10⁻² Pa to 2.7×10⁻² Pa)

Ion accelerating voltage: from 300 to 1,500 V

Film forming rate: from 1.8 to 18.0 nm/min

Here, also in a case where an inert gas other than Ar is used, the above gas pressure applies.

Further, the state before forming the absorber layer of the reflective mask blank for EUVL of the present invention, i.e. the structure having the absorber layer 14 excluded from the reflective mask blank 1 for EUVL shown in FIG. 1, is a substrate with reflective layer for EUVL of the present invention. The substrate with reflective layer for EUVL of the present invention is one constituting a precursor for a reflective mask blank for EUVL. However, the substrate with reflective layer for EUVL of the present invention is not limited to a precursor for a reflective mask blank for EUVL and may generally be useful as an optical substrate having a function to reflect EUV light.

In the substrate with reflective layer for EUVL of the present invention, at least one layer among the respective layers (low refractive index layers and high refractive index layers) constituting the multilayer reflective film is a reflectivity distribution correction layer having a thickness distribution such that the thickness increases or decreases within a range of from 0.1 to 1 nm in a radial direction from the center of the substrate. Such a change in the thickness is more preferably a thickness distribution such that the thickness continuously increases or continuously decreases in a radial direction from the center of the substrate.

Further, in a case where a protective layer is formed on the reflective layer, at least one layer among the protective layer and the respective layers (low refractive index layers and high refractive index layers) constituting the multilayer reflective film is a reflectivity distribution correction layer having a thickness distribution such that the thickness increases or decreases within a range of from 0.1 to 1 nm in a radial direction from the center of the substrate. Also in this case, the change in the thickness is more preferably a thickness distribution such that the thickness continuously increases or continuously decreases in a radial direction from the center of the substrate.

The property particularly required for the absorber layer 14 is that the EUV light reflectivity is very low. Specifically, the maximum light reflectivity in the vicinity of a wavelength of 13.5 nm at the time of irradiating the surface of the absorber layer 14 with a light ray in the wavelength region of EUV light, is preferably at most 0.5%, more preferably at most 0.1%.

In order to attain the above property, the absorber layer 14 is preferably made of a material having a high absorption coefficient of EUV light and is preferably a layer containing at least Ta and N.

Further, the absorber layer 14 being a layer containing at least Ta and N is preferred also from such a viewpoint that it is thereby easy to form a film having a crystalline state being amorphous.

As the layer containing at least Ta and N, it is preferred to employ one member selected from the group consisting of TaN, TaNH, TaBN, TaGaN, TaGeN, TaSiN, TaBSiN and PdTaN. Examples of such preferred compositions for the absorber layer are as follows.

TaN Layer

Content of Ta: preferably from 30 to 90 at %, more preferably from 40 to 80 at %, further preferably from 40 to 70 at %, particularly preferably from 50 to 70 at %

Content of N: preferably from 10 to 70 at %, more preferably from 20 to 60 at %, further preferably from 30 to 60 at %, particularly preferably from 30 to 50 at %

TaNH Layer

Total content of Ta and N: preferably from 50 to 99.9 at %, more preferably from 90 to 98 at %, further preferably from 95 to 98 at %

Content of H: preferably from 0.1 to 50 at %, more preferably from 2 to 10 at %, further preferably from 2 to 5 at %

Compositional ratio of Ta to N (Ta:N): preferably from 9:1 to 3:7, more preferably from 7:3 to 4:6, further preferably from 7:3 to 5:5

TaBN Layer

Total content of Ta and N: preferably from 75 to 95 at %, more preferably from 85 to 95 at %, further preferably from 90 to 95 at %

Content of B: preferably from 5 to 25 at %, more preferably from 5 to 15 at %, further preferably from 5 to 10 at %

Compositional ratio of Ta to N (Ta:N): preferably from 9:1 to 3:7, more preferably from 7:3 to 4:6, further preferably from 7:3 to 5:5

TaBSiN Layer

Content of B: at least 1 at % and less than 5 at %, preferably from 1 to 4.5 at %, more preferably from 1.5 to 4 at %

Content of Si: from 1 to 25 at %, preferably from 1 to 20 at %, more preferably from 2 to 12 at %

Compositional ratio of Ta to N (Ta:N): from 8:1 to 1:1

Content of Ta: preferably from 50 to 90 at %, more preferably from 60 to 80 at %

Content of N: preferably from 5 to 30 at %, more preferably from 10 to 25 at %

PdTaN Layer

Total content of Ta and N: preferably from 30 to 80 at %, more preferably from 30 to 75 at %, further preferably from 30 to 70 at %

Content of Pd: preferably from 20 to 70 at %, more preferably from 25 to 70 at %, further preferably from 30 to 70 at %

Compositional ratio of Ta to N (Ta:N): preferably from 1:7 to 3:1, more preferably from 1:3 to 3:1, further preferably from 3:5 to 3:1

As mentioned above, if the surface roughness of the surface of the absorber layer 14 is large, the edge roughness of a pattern to be formed on the absorber layer 14 tends to be large, and the dimensional precision of the pattern deteriorates. As the pattern becomes fine, the influence of the edge roughness becomes distinct, and therefore, the surface of the absorber layer 14 is required to be smooth.

In a case where a layer containing at least Ta and N is formed as the absorber layer 14, its crystal state is amorphous, and the surface smoothness is excellent. Specifically when a TaN layer is formed as the absorber layer 14, the surface roughness of the surface of the absorber layer 14 becomes to be at most 0.5 nm rms.

When the surface roughness of the surface of the absorber layer 14 is at most 0.5 nm rms, the surface of the absorber layer 14 is sufficiently smooth, whereby the dimensional precision is free from deterioration due to an influence of an edge roughness. The surface roughness of the absorber layer 14 is more preferably at most 0.4 nm rms, further preferably at most 0.3 nm rms.

As a layer containing at least Ta and N, the absorber layer 14 has a high etching rate at the time when dry etching is carried out by using a chlorine-type gas as the etching gas, and shows its etching selectivity to the protective layer 13 being at least 10. In this specification, the etching selectivity can be calculated by the following formula. Etching selectivity=(etching rate of absorber layer 14)/(etching rate of protective layer 13)

The etching selectivity is preferably at least 10, more preferably at least 11, particularly preferably at least 12.

The thickness of the absorber layer 14 is preferably at least 5 nm, more preferably at least 20 nm, further preferably at least 30 nm, particularly preferably at least 50 nm.

On the other hand, if the thickness of the absorber layer 14 is too large, the precision of a pattern to be formed in the absorber layer 14 tends to be low, and therefore, it is preferably at most 100 nm, more preferably at most 90 nm, further preferably at most 80 nm.

For the absorber layer 14, it is possible to use a well-known film-forming method, e.g. a sputtering method such as a magnetron sputtering method or an ion beam sputtering method.

In a case where a TaN layer is to be formed as the absorber layer 14, in the case of using a magnetron sputtering method, the TaN layer may be formed by using a Ta target and letting the target discharge in a nitrogen (N₂) atmosphere diluted by Ar.

In order to form a TaN layer as the absorber layer 14 by the above-exemplified method, specifically the method may be carried out under the following film-forming conditions.

Sputtering gas: mixed gas of Ar and N₂ (N₂ gas concentration: from 3 to 80 vol %, preferably from 5 to 30 vol %, more preferably from 8 to 15 vol %; gas pressure: from 0.5×10⁻¹ Pa to 10×10⁻¹ Pa, preferably from 0.5×10⁻¹ Pa to 5×10⁻¹ Pa, more preferably from 0.5×10⁻¹ Pa to 3×10⁻¹ Pa)

Applied power (for each target): from 30 to 1,000 W, preferably from 50 to 750 W, more preferably from 80 to 500 W

Film forming rate: from 2.0 to 60 nm/min, preferably from 3.5 to 45 nm/min, more preferably from 5 to 30 nm/min.

Further, the reflective mask blank for EUVL of the present invention may have a constituting element other than the construction shown in FIG. 4 (i.e. the substrate 11, the reflective layer 12, the protective layer 13 and the absorber layer 14).

FIG. 4 is a schematic cross-sectional view illustrating another embodiment of the reflective mask blank for EUVL of the present invention.

In the reflective mask blank 1′ for EUVL as shown in FIG. 4, a low reflective layer 15 for inspection light to be used for inspection of a mask pattern is formed on the absorber layer 14.

In the preparation of a reflective mask for EUVL from the reflective mask blank for EUVL of the present invention, after forming a pattern in the absorber layer, inspection is carried out to see that this pattern is formed as designed. In this inspection of the mask pattern, an inspection machine using light of usually 257 nm as inspection light, is employed. That is, the inspection is made by the difference in reflectivity of such light of about 257 nm, specifically by the difference in the reflectivity between a surface exposed by removal of the absorber layer 14 by patterning and the surface of the absorber layer 14 remained without being removed by the patterning. Here, the former is the surface of the protective layer 13, and in a case where no protective layer 13 is formed on the reflective layer 12, it is the surface of the reflective layer 12 (specifically the surface of a Si layer as the uppermost layer of the Mo/Si multilayer reflective film).

Therefore, if the difference in the reflectivity between the protective layer 13 surface (or the reflective layer 12 surface) and the absorber layer 14 surface to the wavelength of inspection light of about 257 nm, is small, the contrast at the time of the inspection becomes poor, and an accurate inspection may not be possible.

The absorber layer 14 having the above-described construction has an extremely low EUV light reflectivity and has excellent properties as an absorber layer for a reflective mask blank for EUVL, but from the viewpoint of the wavelength of inspection light, the light reflectivity may not necessarily be sufficiently low. As a result, the difference between the reflectivity at the absorber layer 14 surface and the reflectivity at the reflective layer 12 surface (or the protective layer 13 surface) at the wavelength of inspection light, tends to be small, and the contrast at the time of inspection may not sufficiently be obtainable. If the contrast at the time of inspection cannot be sufficiently obtained, a defect in the pattern cannot be sufficiently detected in the inspection of a mask, and an accurate inspection of a defect may not be carried out.

Like in the reflective mask blank 1′ for EUVL shown in FIG. 4, by forming a low reflective layer 15 on the absorber layer 14, the contrast at the time of inspection will be good. In other words, the light reflectivity at the wavelength of inspection light becomes very low. With the low reflective layer 15 to be formed for such a purpose, the maximum light reflectivity at the wavelength of inspection light when irradiated with light in the wavelength region (in the vicinity of 257 nm) of inspection light, is preferably at most 15%, more preferably at most 10%, further preferably at most 5%.

When the light reflectivity at the wavelength of inspection light at the low reflective layer 15 is at most 15%, the contrast at the time of the inspection will be good. Specifically, the contrast between reflected light with a wavelength of the inspection light at the protective layer 13 surface (or the reflective layer 12 surface) and reflected light with the wavelength of the inspection light at the low reflective layer 15 surface becomes at least 40%.

In this specification, the contrast is obtained by using the following formula. Contrast(%)=((R ₂ −R ₁)/(R ₂ +R ₁))×100

Here, R₂ at the wavelength of the inspection light is the reflectivity at the protective layer 13 surface (or the reflective layer 12 surface), and R₁ is the reflectivity at the surface of the low reflective layer 15. Here, the above R₁ and R₂ are measured in such a state that a pattern is formed in the absorber layer 14 and the low reflective layer 15 of the reflective mask blank 1′ for EUVL shown in FIG. 4. The above R₂ is a value measured at the protective layer 13 surface (or the reflective layer 12 surface) exposed as the absorber layer 14 and the low reflective layer 15 were removed by patterning, and R₁ is a value measured at the surface of the low reflective layer 15 remained without being removed by patterning.

In the present invention, the contrast represented by the above formula is more preferably at least 45%, further preferably at least 60%, particularly preferably at least 70%.

To attain the above-described properties, the low reflective layer 15 is preferably constituted by a material having a refractive index lower than the absorber layer 14 at the wavelength of inspection light, and its crystal state is preferably amorphous.

As a specific example of such a low reflective layer 15, one containing Ta, oxygen (O) and nitrogen (N) in the following atomic ratio (low reflective layer (TaON)) may be mentioned.

Content of Ta: from 20 to 80 at %, preferably from 20 to 70 at %, more preferably from 20 to 60 at %

Total content of O and N: from 20 to 80 at %, preferably from 30 to 80 at %, more preferably from 40 to 80 at %

Compositional ratio of O to N: from 20:1 to 1:20, preferably from 18:1 to 1:18, more preferably from 15:1 to 1:15

With the above-described construction, the low reflective layer (TaON) is amorphous in its crystal state and is excellent in its surface smoothness. Specifically, the surface roughness of the low reflective layer (TaON) surface is at most 0.5 nm rms.

As mentioned above, in order to prevent deterioration in the dimensional precision of a pattern due to an influence of the edge roughness, it is required that the absorber layer 14 surface is smooth. The low reflective layer 15 is formed on the absorber layer 15, and therefore, for the same reason, its surface is required to be smooth.

When the surface roughness of the low reflective layer 15 surface is at most 0.5 nm rms, the low reflective layer 15 surface is sufficiently smooth and free from deterioration in the dimensional precision of a pattern due to an influence of the edge roughness. The surface roughness of the low reflective layer 15 surface is more preferably at most 0.4 nm rms, further preferably at most 0.3 nm rms.

In a case where the low reflective layer 15 is formed on the absorber layer 14, the total thickness of the absorber layer 14 and the low reflective layer 15 is preferably from 20 to 130 nm. Further, if the thickness of the low reflective layer 15 is more than the thickness of the absorber layer 14, the EUV absorbing property at the absorber layer 14 is likely to be low, and therefore, the thickness of the low reflective layer 15 is preferably less than the thickness of the absorber layer 14. For this reason, the thickness of the low reflective layer 15 is preferably from 5 to 30 nm, more preferably from 10 to 20 nm.

The low reflective layer (TaON) having the above construction may be formed by a sputtering method such as a magnetron sputtering method or an ion beam sputtering method by using a Ta target in an atmosphere of oxygen (O₂) and nitrogen (N₂) diluted with an inert gas containing at least one of helium (He), argon (Ar), neon (Ne), krypton (Kr) and xenon (Xe). Otherwise, a Ta target may be discharged in a nitrogen (N₂) atmosphere diluted with an inert gas containing at least one of helium (He), argon (Ar), neon (Ne), krypton (Kr) and xenon (Xe) to form a film containing Ta and N, and then the formed film is oxidized by e.g. being exposed to oxygen plasma or being irradiated with an ion beam using oxygen, to obtain the low reflective layer (TaON) having the above construction.

In order to form the low reflective layer (TaON) by the above method, specifically the following film-forming conditions may be employed.

Sputtering gas: mixed gas of Ar, O₂ and N₂ (O₂ gas concentration: from 5 to 80 vol %, N₂ gas concentration: from 5 to 75 vol %, preferably O₂ gas concentration: from 6 to 70 vol %, N₂ gas concentration: from 6 to 35 vol %, more preferably O₂ gas concentration: from 10 to 30 vol %, N₂ gas concentration: from 10 to 30 vol %, Ar gas concentration: from 5 to 90 vol %, preferably from 10 to 88 vol %, more preferably from 20 to 80 vol %; gas pressure: from 1.0×10⁻¹ Pa to 50×10⁻¹ Pa, preferably from 1.0×10⁻¹ Pa to 40×10⁻¹ Pa, more preferably from 1.0×10⁻¹ Pa to 30×10⁻¹ Pa)

Applied power: from 30 to 1,000 W, preferably from 50 to 750 W, more preferably from 80 to 500 W

Film forming rate: from 0.1 to 50 nm/min, preferably from 0.2 to 45 nm/min, more preferably from 0.2 to 30 nm/min.

Here, in a case where an inert gas other than Ar is used, the concentration of such an inert gas is adjusted to be within the same concentration range as the above Ar gas concentration. Further, in a case where plural types of inert gases are used, the total concentration of such inert gases is adjusted to be within the same concentration range as the above Ar gas concentration.

Here, the reason as to why it is preferred to form a low reflective layer 15 on the absorber layer 14 as in the reflective mask blank 1′ for EUVL shown in FIG. 5, is that the wavelength of inspection light for a pattern is different from the wavelength of EUV light. Therefore, in a case where EUV light (in the vicinity of 13.5 nm) is used as the inspection light for a pattern, it is considered unnecessary to form a low reflective layer 15 on the absorber layer 14. The wavelength of inspection light tends to be shifted toward a low wavelength side as the size of a pattern becomes small, and in future, it is considered to be shifted to 193 nm or further to 13.5 nm. Further, in the case where the wavelength of inspection light is 193 nm, it may not be required to form a low reflective layer 15 on the absorber layer 14. In the case where the wavelength of inspection light is 13.5 nm, it is considered unnecessary to form a low reflective layer 15 on the absorber layer 14.

The reflective mask blank for EUVL of the present invention may have a functional film commonly known in the field of reflective mask blanks for EUVL, in addition to the reflective layer 12, the protective layer 13, the absorber layer 14 and the low reflective layer 15. A specific example of such a functional film may, for example, be an electrically conductive coating formed on the rear side of a substrate to promote the electrostatic chucking of the substrate, as disclosed in e.g. JP-A-2003-501823. Here, in the substrate 11 shown in FIG. 1, the rear side of the substrate means the surface on the opposite side to the side where the reflective layer 12 is formed. For the electrically conductive coating to be formed on the rear side of the substrate for such a purpose, the electrical conductivity and the thickness of the constituting material are selected so that the sheet resistance will be at most 100Ω/□. The constituting material of the electrically conductive coating may be selected widely from those disclosed in known literatures. For example, an electrically conductive (high dielectric constant) coating disclosed in JP-A-2003-501823, specifically a coating comprising silicon, TiN, molybdenum, chromium and TaSi may be applied. The thickness of the electrically conductive coating may, for example, be from 10 to 1,000 nm.

The electrically conductive coating may be formed by means of a known film-forming method e.g. a sputtering method, such as a magnetron sputtering method or an ion beam sputtering method, a CVD method, a vacuum vapor deposition method or an electroplating method.

In the reflective mask blank for EUVL of the present invention, at least one layer among the respective layers (low refractive index layers and high refractive index layers) constituting the multilayer reflective film is a reflectivity distribution correction layer having a thickness distribution such that the thickness increases or decreases within a range of from 0.1 to 1 nm in a radial direction from the center of the substrate. Such a change in the thickness is more preferably a thickness distribution such that the thickness continuously increases or continuously decreases in a radial direction from the center of the substrate.

Further, in a case where a protective layer is formed on the reflective layer, at least one layer among the respective layers (low refractive index layers and high refractive index layers) constituting the multilayer reflective film and the protective layer is a reflectivity distribution correction layer having a thickness distribution such that the thickness increases or decreases within a range of from 0.1 to 1 nm in a radial direction from the center of the substrate. Also in this case, the change in the thickness is more preferably a thickness distribution such that the thickness continuously increases or continuously decreases in a radial direction from the center of the substrate.

The reflective mask for EUVL may be produced by patterning at least the absorber layer of the reflective mask blank for EUVL produced by the process of the present invention (in a case where a low reflective layer is formed on the absorber layer, the absorber layer and the low reflective layer). The method for patterning the absorber layer (in a case where a low reflective layer is formed on the absorber layer, the absorber layer and the low reflective layer), is not particularly limited. For example, a method may be employed wherein a resist is applied on the absorber layer (in a case where a low reflective layer is formed on the absorber layer, the absorber layer and the low reflective layer) to form a resist pattern, and by using it as a mask, the absorber layer (in a case where a low reflective layer is formed on the absorber layer, the absorber layer and the low reflective layer) is subjected to etching. The material for the resist, or the drawing method for the resist pattern may suitably be selected in consideration of e.g. the material of the absorber layer (in a case where a low reflective layer is formed on the absorber layer, the absorber layer and the low reflective layer). As the method for etching the absorber layer (in a case where a low reflective layer is formed on the absorber layer, the absorber layer and the low reflective layer), dry etching using a chlorine-type gas as an etching gas may be employed. After patterning the absorber layer (in a case where a low reflective layer is formed on the absorber layer, the absorber layer and the low reflective layer), the resist is removed by a remover liquid to obtain the reflective mask for EUVL.

EXAMPLES

Now, the present invention will be described in further detail with reference to Examples.

Comparative Example 1

In this Example, a substrate with reflective layer for EUVL was prepared. This substrate with reflective layer for EUVL has a structure having the absorber layer 14 excluded from the mask blank 1 shown in FIG. 1.

As a substrate 11 for film formation, a SiO₂—TiO₂ type glass substrate (size: 6 inches (152 mm) square, thickness: 6.35 mm) is used. The thermal expansion coefficient of this glass substrate is 0.05×10⁻⁷/° C., the Young's modulus is 67 GPa, the Poisson ratio is 0.17, and the specific rigidity is 3.07×10⁷ m²/s². This glass substrate was polished to form a smooth surface having a surface roughness rms of at most 0.15 nm and a planarity of at most 100 nm.

On the rear surface side of the substrate 11, a Cr film having a thickness of 100 nm was formed by a magnetron sputtering method to provide an electrically conductive coating (not shown in the drawings) having a sheet resistance of 100Ω/□.

By using the Cr film formed by the above procedure, the substrate 11 (size: 6 inches (152 mm) square, thickness: 6.35 mm) was fixed to a usual electrostatic chuck of a flat plate shape, and on the surface of the substrate 11, by carrying out the spinning film formation as shown in FIG. 2, a Mo film and a Si film were alternately formed by means of an ion beam sputtering method for 40 cycles to form a Mo/Si multilayer reflective film (reflective layer 12) having a total thickness of 280 nm ((2.5 nm+4.5 nm)×40). Here, the uppermost layer of the Mo/Si multilayer reflective film is a Si film. The Mo/Si multilayer reflective layer was formed in a 152 mm square region on the substrate 11 surface.

The film forming conditions for the Mo film and the Si film are as follows.

Film Forming Conditions for Mo Film

-   -   Target: Mo target     -   Sputtering gas: mixed gas of Ar and H₂ (H₂ gas concentration: 3         vol %, Ar gas concentration: 97 vol %, gas pressure: 0.02 Pa)     -   Voltage: 700 V     -   Film forming rate: 3.84 nm/min.     -   Film thickness: 2.3 nm         Film Forming Conditions for Si Film     -   Target: Si target (boron-doped)     -   Sputtering gas: mixed gas of Ar and H₂ (H₂ gas concentration: 3         vol %, Ar gas concentration: 97 vol %, gas pressure: 0.02 Pa)     -   Voltage: 700 V     -   Film forming rate: 4.62 nm/min.     -   Film thickness: 4.5 nm

With respect to the Si layer as the uppermost layer in the Mo/Si multilayer reflective film formed by the above procedure, the thickness distribution in a radial direction from the center of the substrate was evaluated by means of XRR (X-ray reflectivity method). The thickness distribution in a radial direction from the center of the substrate was 0.0 nm.

To the surface of the Mo/Si multilayer reflective film formed by the above procedure, EUV light was applied at an incident angle of 6°. Reflected light in the EUV wavelength region at that time was measured by means of an EUV reflectivity meter (MBR, manufactured by AIXUV GmbH), whereupon the in-plane distribution of the peak reflectivity in the same wavelength region and the in-plane distribution of the center wavelength of reflected light were evaluated.

The in-plane distribution of the center wavelength of reflected light in the EUV wavelength region was within 0.04 nm, which satisfies the required value relating to the in-plane uniformity of the center wavelength of reflected light in the EUV wavelength region, i.e. its range (the difference between the maximum value and the minimum value of the center wavelength) being within 0.06 nm. Here, the in-plane distribution of the center wavelength of reflected light in the EUV wavelength region being within 0.04 nm, corresponds to the thickness distribution of the bilayer composed of two layers of a Mo layer and a Si layer, as the basic structure of the Mo/Si multilayer film, being 0.04/13.53≈0.3%.

On the other hand, “Before correction” (dashed line) in FIG. 5 is a graph showing the relation between the location in a radial direction from the center of the substrate and the in-plane distribution of the peak reflectivity of EUV light, when EUV light was applied at an incident angle of 6° to the Mo/Si multilayer reflective film formed by the above procedure.

As shown by “Before correction” (dashed line) in FIG. 5, an in-plane distribution is observed such that the peak reflectivity of EUV light lowers from the center of the substrate towards the peripheral portion of the substrate. The in-plane distribution of the peak reflectivity of EUV light exceeds 0.6%, which does not satisfy the required value relating to the in-plane uniformity of the peak reflectivity of EUV light, i.e. its range (the difference between the maximum value and the minimum value of the center wavelength) being within 0.5%.

Example 1

In this Example, a Mo/Si multilayer reflective film was formed as a reflective layer 2 on a substrate 11 in the same manner as in Comparative Example 1 except that a Si layer as the uppermost layer in the Mo/Si multilayer reflective film was made to be a reflectivity distribution correction layer having a thickness distribution provided in a radial direction, based on the in-plane distribution of the peak reflectivity of light in the EUV wavelength region obtained in Comparative Example 1 (“Before correction” in FIG. 5) and the thickness dependency of the peak reflectivity of EUV light shown in FIG. 3. Specifically the procedure was as follows.

The thickness of the reflection distribution correction layer (Si layer) at the peripheral portion of the substrate where the peak reflectivity of EUV light became lowest in Comparative Example 1, was set to be (4.5 nm) in the vicinity of the thickness where the peak reflectivity of EUV light becomes to have a local maximum value in FIG. 3. On the other hand, at the center of the substrate where the peak reflectivity became highest in Comparative Example 1, the thickness was adjusted to the thickness (4.9 nm) corresponding to the decrease amount (about 0.6%) of the peak reflectivity of EUV light from the center towards the peripheral portion of the substrate.

With respect to the reflectivity distribution correction layer (Si layer) in the Mo/Si multilayer reflective film formed by the above procedure, the thickness distribution in a radial direction from the center of the substrate was evaluated by means of XRR (X-ray reflectivity method). The thickness distribution in a radial direction from the center of the substrate was 0.4 nm, which substantially agreed to the difference between the thickness at the above substrate peripheral portion and the thickness at the center of the substrate.

As shown by “After correction” (solid line) in FIG. 5, as the Si layer as the uppermost layer in the Mo/Si multilayer reflective film was made to be a reflectivity distribution correction layer having a thickness distribution provided, the in-plane distribution of the peak reflectivity such that the peak reflectivity of EUV light lowers in a radial direction from the center of the substrate towards the peripheral portion, was suppressed, and the in-plane distribution of the peak reflectivity became to be about 0.1%.

Comparative Example 2

In the same manner as in Comparative Example 1, a Mo/Si multilayer reflective film was formed on a substrate, and the relation between the location in a radial direction from the center of the substrate and the in-plane distribution of the peak reflectivity of EUV light, when EUV light was applied at an incident angle of 6° to the Mo/Si multilayer reflective film, was evaluated. “Before correction” (dashed line) in FIG. 6 is a graph showing the relation between the location in a radial direction from the center of the substrate and the in-plane distribution of the peak reflectivity of EUV light.

As shown by “Before correction” (dashed line) in FIG. 6, an in-plane distribution is observed such that the peak reflectivity of EUV light lowers from the center of the substrate towards the peripheral portion of the substrate. The in-plane distribution of the peak reflectivity of EUV light exceeds 0.6%, which does not satisfy the required value relating to the in-plane uniformity of the peak reflectivity of EUV light, i.e. its range (the difference between the maximum value and the minimum value of the center wavelength) being within 0.5%.

Example 2

In this Example, the 3rd Si layer in the stacked number of repeating units of a low refractive index layer (a Mo layer) and a high refractive index layer (a Si layer) from the uppermost layer in the Mo/Si multilayer reflective film (i.e. the 3rd Si layer from the top) was made to be a reflectivity distribution correction layer having a thickness distribution provided in a radial direction.

The thickness of the reflection distribution correction layer (Si layer) at the peripheral portion of the substrate where the peak reflectivity of EUV light became lowest in Comparative Example 2, was set to be (4.5 nm) in the vicinity of the thickness where the peak reflectivity of EUV light becomes to have a local maximum value. On the other hand, at the center of the substrate where the peak reflectivity became highest in Comparative Example 2, the thickness was adjusted to the thickness (4.9 nm) corresponding to the decrease amount (about 0.6%) of the peak reflectivity of EUV light from the center towards the peripheral portion of the substrate.

As shown by “After correction” (solid line) in FIG. 6, as the 3rd Si layer from the top in the Mo/Si multilayer reflective film was made to be a reflectivity distribution correction layer having a thickness distribution provided in a radial direction, the in-plane distribution of the peak reflectivity such that the peak reflectivity of EUV light lowers in a radial direction from the center of the substrate towards the peripheral portion, was suppressed, and the in-plane distribution of the peak reflectivity became to be about 0.1%.

Comparative Example 3

In the same manner as in Comparative Example 1, a Mo/Si multilayer reflective film was formed on a substrate, and the relation between the location in a radial direction from the center of the substrate and the in-plane distribution of the peak reflectivity of EUV light, when EUV light was applied at an incident angle of 6° to the Mo/Si multilayer reflective film, was evaluated. “Before correction” (dashed line) in FIG. 7 is a graph showing the relation between the location in a radial direction from the center of the substrate and the in-plane distribution of the peak reflectivity of EUV light.

As shown by “Before correction” (dashed line) in FIG. 7, an in-plane distribution is observed such that the peak reflectivity of EUV light lowers from the center of the substrate towards the peripheral portion of the substrate. The in-plane distribution of the peak reflectivity of EUV light was about 0.4%.

Example 3

In this Example, the 10th Si layer in the stacked number of repeating units of a low refractive index layer (a Mo layer) and a high refractive index layer (a Si layer) from the uppermost layer in the Mo/Si multilayer reflective film (i.e. the 10th Si layer from the top) was made to be a reflectivity distribution correction layer having a thickness distribution provided in a radial direction.

The thickness of the reflection distribution correction layer (Si layer) at the peripheral portion of the substrate where the peak reflectivity of EUV light became lowest in Comparative Example 3, was set to be (4.5 nm) in the vicinity of the thickness where the peak reflectivity of light in the EUV wavelength region becomes to have a local maximum value. On the other hand, at the center of the substrate where the peak reflectivity became highest in Comparative Example 3, the thickness was adjusted to the thickness (4.9 nm) corresponding to the decrease amount (about 0.4%) of the peak reflectivity of EUV light from the center towards the peripheral portion of the substrate.

As shown by “After correction” (solid line) in FIG. 7, as the 10th Si layer from the top in the Mo/Si multilayer reflective film was made to be a reflectivity distribution correction layer having a thickness distribution provided in a radial direction, the in-plane distribution of the peak reflectivity such that the peak reflectivity of EUV light lowers in a radial direction from the center of the substrate towards the peripheral portion, was suppressed, and the in-plane distribution of the peak reflectivity became to be about 0.1%.

Comparative Example 4

In the same manner as in Comparative Example 1, a Mo/Si multilayer reflective film was formed on a substrate, and the relation between the location in a radial direction from the center of the substrate and the in-plane distribution of the peak reflectivity of EUV light, when EUV light was applied at an incident angle of 6° to the Mo/Si multilayer reflective film, was evaluated. “Before correction” (dashed line) in FIG. 8 is a graph showing the relation between the location in a radial direction from the center of the substrate and the in-plane distribution of the peak reflectivity of EUV light.

As shown by “Before correction” (dashed line) in FIG. 8, an in-plane distribution is observed such that the peak reflectivity of EUV light lowers from the center of the substrate towards the peripheral portion of the substrate. The in-plane distribution of the peak reflectivity of EUV light exceeds 1.6%, which does not satisfy the required value relating to the in-plane uniformity of the peak reflectivity of EUV light, i.e. its range (the difference between the maximum value and the minimum value of the center wavelength) being within 0.5%.

Example 4

In this Example, a Si layer as the uppermost layer in the Mo/Si multilayer reflective film and the 2nd Si layer in the stacked number of repeating units of a low refractive index layer (a Mo layer) and a high refractive index layer (a Si layer) from the uppermost layer (i.e. the 2nd Si layer from the top) were made to be reflectivity distribution correction layers each having a thickness distribution provided in a radial direction.

The thickness of each reflection distribution correction layer (Si layer) at the peripheral portion of the substrate where the peak reflectivity of EUV light became lowest in Comparative Example 1, was set to be (4.5 nm) in the vicinity of the thickness where the peak reflectivity of light in the EUV wavelength region becomes to have a local maximum value. On the other hand, at the center of the substrate where the peak reflectivity became highest in Comparative Example 1, the thickness was adjusted to the thickness (4.9 nm) corresponding to the decrease amount (about 1.6%) of the peak reflectivity of light in the EUV wavelength region from the center towards the peripheral portion of the substrate.

As shown by “After correction” (solid line) in FIG. 8, as the uppermost layer and the 2nd Si layer from the top in the Mo/Si multilayer reflective film were made to be reflectivity distribution correction layers each having a thickness distribution provided in a radial direction, the in-plane distribution of the peak reflectivity such that the peak reflectivity of light in the EUV wavelength region lowers in a radial direction from the center of the substrate towards the peripheral portion, was suppressed, and the in-plane distribution of the peak reflectivity became to be about 0.3%.

REFERENCE SYMBOLS

-   -   1, 1′: EUV mask blank     -   11: Substrate     -   12: Reflective layer (Mo/Si multilayer reflective film)     -   13: Protective layer     -   14: Absorber layer     -   15: Low reflective layer     -   20: Sputtered particles     -   30: Center axis

The entire disclosure of Japanese Patent Application No. 2012-155453 filed on Jul. 11, 2012 including specification, claims, drawings and summary is incorporated herein by reference in its entirety. 

What is claimed is:
 1. A process for producing a substrate with reflective layer for EUV lithography (EUVL), which comprises forming a reflective layer for reflecting EUV light on a substrate, wherein the reflective layer is a multilayer reflective film having a low refractive index layer and a high refractive index layer alternately stacked plural times by a sputtering method, and depending upon the in-plane distribution of the peak reflectivity of light in the EUV wavelength region in a radial direction from the center of the substrate at the surface of the multilayer reflective film, at least one layer among the respective layers constituting the multilayer reflective film is made to be a reflectivity distribution correction layer having a thickness distribution provided in a radial direction from the center of the substrate, to suppress and reduce the in-plane distribution of the peak reflectivity of light in the EUV wavelength region in a radial direction from the center of the substrate.
 2. A process for producing a substrate with reflective layer for EUV lithography (EUVL), which comprises forming a reflective layer for reflecting EUV light on a substrate, and forming a protective layer for the reflective layer on the reflective layer, wherein the reflective layer is a multilayer reflective film having a low refractive index layer and a high refractive index layer alternately stacked plural times by a sputtering method, the protective layer is a Ru layer or a Ru compound layer formed by a sputtering method, and depending upon the in-plane distribution of the peak reflectivity of light in the EUV wavelength region in a radial direction from the center of the substrate at the surface of the protective layer, at least one layer among the respective layers constituting the multilayer reflective film and the protective layer, is made to be a reflectivity distribution correction layer having a thickness distribution provided in a radial direction from the center of the substrate, to suppress and reduce the in-plane distribution of the peak reflectivity of light in the EUV wavelength region in a radial direction from the center of the substrate.
 3. The process for producing a substrate with reflective layer for EUVL according to claim 1, wherein the in-plane distribution of the peak reflectivity of light in the EUV wavelength region in a radial direction from the center of the substrate in a case where the thickness distribution corresponding to the reflectivity distribution correction layer is not provided, is an in-plane distribution such that the peak reflectivity becomes low in a radial direction from the center of the substrate, and as the thickness distribution in a radial direction from the center of the substrate in the reflectivity distribution correction layer, a thickness distribution such that the peak reflectivity of light in the EUV wavelength region becomes high in a radial direction from the center of the substrate, is provided, to suppress and reduce the in-plane distribution of the peak reflectivity of light in the EUV wavelength region in a radial direction from the center of the substrate.
 4. The process for producing a substrate with reflective layer for EUVL according to claim 2, wherein the in-plane distribution of the peak reflectivity of light in the EUV wavelength region in a radial direction from the center of the substrate in a case where the thickness distribution corresponding to the reflectivity distribution correction layer is not provided, is an in-plane distribution such that the peak reflectivity becomes low in a radial direction from the center of the substrate, and as the thickness distribution in a radial direction from the center of the substrate in the reflectivity distribution correction layer, a thickness distribution such that the peak reflectivity of light in the EUV wavelength region becomes high in a radial direction from the center of the substrate, is provided, to suppress and reduce the in-plane distribution of the peak reflectivity of light in the EUV wavelength region in a radial direction from the center of the substrate.
 5. The process for producing a substrate with reflective layer for EUVL according to claim 3, wherein the thickness of the reflectivity distribution correction layer is adjusted to be such a thickness that at the peripheral portion of the substrate, the peak reflectivity of light in the EUV wavelength region becomes to have a local maximum value, and the difference between the thickness of the reflectivity distribution correction layer at the peripheral portion of the substrate and the thickness of the reflectivity distribution correction layer at the center of the substrate, is set so that the difference between the maximum value and the minimum value of the peak reflectivity in the in-plane distribution of the peak reflectivity of light in the EUV wavelength region in a radial direction from the center of the substrate in a case where the reflectivity distribution correction layer is provided, becomes to be at most 0.3%.
 6. The process for producing a substrate with reflective layer for EUVL according to claim 4, wherein the thickness of the reflectivity distribution correction layer is adjusted to be such a thickness that at the peripheral portion of the substrate, the peak reflectivity of light in the EUV wavelength region becomes to have a local maximum value, and the difference between the thickness of the reflectivity distribution correction layer at the peripheral portion of the substrate and the thickness of the reflectivity distribution correction layer at the center of the substrate, is set so that the difference between the maximum value and the minimum value of the peak reflectivity in the in-plane distribution of the peak reflectivity of light in the EUV wavelength region in a radial direction from the center of the substrate in a case where the reflectivity distribution correction layer is provided, becomes to be at most 0.3%.
 7. The process for producing a substrate with reflective layer for EUVL according to claim 5, wherein the change in the peak reflectivity of light in the EUV wavelength region in a radial direction from the center of the substrate, formed by the thickness distribution in a radial direction from the center of the substrate, in the reflectivity distribution correction layer, is within 2%.
 8. The process for producing a substrate with reflective layer for EUVL according to claim 6, wherein the change in the peak reflectivity of light in the EUV wavelength region in a radial direction from the center of the substrate, formed by the thickness distribution in a radial direction from the center of the substrate, in the reflectivity distribution correction layer, is within 2%.
 9. The process for producing a substrate with reflective layer for EUVL according to claim 1, wherein in the multilayer reflective film, the stacked number of repeating units of the low refractive index layer and the high refractive index layer is from 30 to 60, and at least one layer among layers formed by the stacked number of repeating units being at most 20 from the uppermost layer of the multilayer reflective film, is made to be the reflectivity distribution correction layer.
 10. The process for producing a substrate with reflective layer for EUVL according to claim 2, wherein in the multilayer reflective film, the stacked number of repeating units of the low refractive index layer and the high refractive index layer is from 30 to 60, and at least one layer among the protective layer and layers formed by the stacked number of repeating units being at most 20 from the uppermost layer of the multilayer reflective film, is made to be the reflectivity distribution correction layer.
 11. The process for producing a substrate with reflective layer for EUVL according to claim 1, wherein the multilayer reflective film is a Mo/Si multilayer reflective film having a molybdenum (Mo) layer and a silicon (Si) layer alternately stacked plural times, and at least one layer among Si layers in the Mo/Si multilayer reflective film is made to be the reflectivity distribution correction layer.
 12. The process for producing a substrate with reflective layer for EUVL according to claim 2, wherein the multilayer reflective film is a Mo/Si multilayer reflective film having a molybdenum (Mo) layer and a silicon (Si) layer alternately stacked plural times, and at least one layer among Si layers in the Mo/Si multilayer reflective film is made to be the reflectivity distribution correction layer.
 13. The process for producing a substrate with reflective layer for EUVL according to claim 11, wherein a Si layer as the uppermost layer among Si layers in the Mo/Si multilayer reflective film is made to be the reflectivity distribution correction layer.
 14. The process for producing a substrate with reflective layer for EUVL according to claim 12, wherein a Si layer as the uppermost layer among Si layers in the Mo/Si multilayer reflective film is made to be the reflectivity distribution correction layer.
 15. A substrate with reflective layer for EUVL, produced by the process for producing a substrate with reflective layer for EUVL as defined in claim
 1. 16. A substrate with reflective layer for EUVL, produced by the process for producing a substrate with reflective layer for EUVL as defined in claim
 2. 17. A substrate with reflective layer for EUV lithography (EUVL), which comprises a substrate and a reflective layer for reflecting EUV light formed on the substrate, wherein the reflective layer is a multilayer reflective film having a low refractive index layer and a high refractive index layer alternately stacked plural times, and at least one layer among the respective layers constituting the multilayer reflective film is a reflectivity distribution correction layer having a thickness distribution such that the thickness increases or decreases within a range of from 0.1 to 1 nm in a radial direction from the center of the substrate.
 18. A substrate with reflective layer for EUV lithography (EUVL), which comprises a substrate, a reflective layer for reflecting EUV light formed on the substrate, and a protective layer for the reflective layer formed on the reflective layer, wherein the reflective layer is a multilayer reflective film having a low refractive index layer and a high refractive index layer alternately stacked plural times, and at least one layer among the respective layers constituting the multilayer reflective film and the protective layer is a reflectivity distribution correction layer having a thickness distribution such that the thickness increases or decreases within a range of from 0.1 to 1 nm in a radial direction from the center of the substrate.
 19. The substrate with reflective layer for EUVL according to claim 17, wherein the multilayer reflective film is a Mo/Si multilayer reflective film having a molybdenum (Mo) layer and a silicon (Si) layer alternately stacked plural times, and at least one layer among Si layers in the Mo/Si multilayer reflective film is the reflectivity distribution correction layer.
 20. The substrate with reflective layer for EUVL according to claim 18, wherein the multilayer reflective film is a Mo/Si multilayer reflective film having a molybdenum (Mo) layer and a silicon (Si) layer alternately stacked plural times, and at least one layer among Si layers in the Mo/Si multilayer reflective film is the reflectivity distribution correction layer.
 21. The substrate with reflective layer for EUVL according to claim 19, wherein a Si layer as the uppermost layer among Si layers in the Mo/Si multilayer reflective film is the reflectivity distribution correction layer.
 22. The substrate with reflective layer for EUVL according to claim 20, wherein a Si layer as the uppermost layer among Si layers in the Mo/Si multilayer reflective film is the reflectivity distribution correction layer.
 23. A reflective mask blank for EUV lithography (EUVL), which comprises a substrate, a reflective layer for reflecting EUV light formed on the substrate, and an absorber layer for absorbing EUV light formed on the reflective layer, wherein the reflective layer is a multilayer reflective film having a low refractive index layer and a high refractive index layer alternately stacked plural times, and at least one layer among the respective layers constituting the multilayer reflective film is a reflectivity distribution correction layer having a thickness distribution such that the thickness increases or decreases within a range of from 0.1 to 1 nm in a radial direction from the center of the substrate.
 24. A reflective mask blank for EUV lithography (EUVL), which comprises a substrate, a reflective layer for reflecting EUV light formed on the substrate, a protective layer for the reflective layer formed on the reflective layer, and an absorber layer for absorbing EUV light formed on the protective layer, wherein the reflective layer is a multilayer reflective film having a low refractive index layer and a high refractive index layer alternately stacked plural times, the protective layer is a Ru layer or a Ru compound layer, and at least one layer among the respective layers constituting the multilayer reflective film and the protective layer is a reflectivity distribution correction layer having a thickness distribution such that the thickness increases or decreases within a range of from 0.1 to 1 nm in a radial direction from the center of the substrate.
 25. The reflective mask blank for EUVL according to claim 23, wherein the multilayer reflective film is a Mo/Si multilayer reflective film having a molybdenum (Mo) layer and a silicon (Si) layer alternately stacked plural times, and at least one layer among Si layers in the Mo/Si multilayer reflective film is the reflectivity distribution correction layer.
 26. The reflective mask blank for EUVL according to claim 24, wherein the multilayer reflective film is a Mo/Si multilayer reflective film having a molybdenum (Mo) layer and a silicon (Si) layer alternately stacked plural times, and at least one layer among Si layers in the Mo/Si multilayer reflective film is the reflectivity distribution correction layer.
 27. The reflective mask blank for EUVL according to claim 25, wherein a Si layer as the uppermost layer among Si layers in the Mo/Si multilayer reflective film is the reflectivity distribution correction layer.
 28. The reflective mask blank for EUVL according to claim 26, wherein a Si layer as the uppermost layer among Si layers in the Mo/Si multilayer reflective film is the reflectivity distribution correction layer. 